This invention relates to a method for making molds.
One of the conventional methods for making molds comprises forming a metal pattern, heating the metal pattern to an elevated temperature, applying a molding material including a thermosetting resin therein to the heated metal pattern, thereby hardening the molding material by heat conduction from the heated metal pattern, and finally separating the metal pattern from the hardened molding material. In this method, however, since the pattern is made of metal, the cost for making the pattern will necessarily become expensive and it is difficult to produce a complicated pattern shape. Besides, the molding material is hardened by the heat conduction from the metal pattern which produces a great deal of energy loss. Therefore, poor energy efficiency is obtained.
Another conventional method for making molds includes forming a metal pattern, heating the metal pattern to an elevated temperature of about 250.degree. C., coating a powdered facing agent on the heated metal pattern by spraying, applying a molding material including a thermosetting resin therein to the facing agent coated and still heated metal pattern, thereby hardening the molding material by heat conduction from the heated metal pattern, and finally separating the metal pattern from the hardened molding material.
The casting surface of cast product produced by using this mold is very fine and it is possible to obtain a roughness of 200 RMS for aluminum and 300 RMS for FC material of Japanese Industrial Standard. This method too, however, has the same problems associated with the metal pattern described above. Besides, this method has the following problems. First, since a powdered facing agent is employed, it is difficult to effectively coat a pattern having a complicated shape. Secondly, since it is necessary to spray the powdered facing agent in a direction perpendicular to the surface of the metal pattern, a special spraying device must be employed. Thirdly, in the case of employing shell mold sand, the coated facing agent will likely be blown off.